Normally, an immersion lance having one conduit which delivers the powdered reagent to the molten metal bath is utilized for the process of treating the metals. In this instance the exit port of the conduit which is positioned in the molten metal bath may get clogged with solidified metal or slag and thus reduces the life of the immersion lance requiring the lance to be replaced and disrupting the treatment of the metal. A dual port lance was introduced to overcome the limitations of the single port lance. The conventional dual port lance contains one conduit which branches off into two or more exit ports that are immersed into the metal bath. With a conventional dual port lance, it is nearly impossible to keep equal flows to both ports. Consequently, one port gets a reduced flow of gas/solids. This allows liquid metal to penetrate the port and freeze, further restricting flow through that port. In a matter of minutes the port plugs with metal, leaving the operator with a single port lance with excessive gas flows. Thus, the conventional dual port lance is also susceptible to slag or solidified metal clogging the exit ports of the feed tube. That increased flow would create unacceptable splash and turbulence and possibly cause unacceptable distribution of injected material. An increase in the pressure into the conduit was thought to be able to keep the flow path in the conduit clear, but this resulted in an unacceptable splash in the molten metal bath.
In order to overcome the limitations of unacceptable splash and clogging of the conduits of the conventional lances, the present invention provides multiple conduits each having independently controlled pressure streams of the powdered reagent. The structure of the present invention eliminates the problem of clogging of the dual port lance conduits because there is no venting of the pressure stream from a clogged port to a clear exit port, thus no unacceptable splash will occur. When solidified metal or slag obstructs an exit port of the present invention the line pressure will increase and usually clear the obstruction. Once the obstruction in the exit port is cleared, the pressure will return to the initial pressure. Furthermore, if necessary the flow rate into the conduit can be increased manually to clear an obstruction that is detected by a monitoring system, thus resulting in the removal of the obstruction. After the obstruction is removed the pressure can be decreased manually to the initial pressure. Admittedly, the exit ports may get clogged in a way that no amount of pressure will remove the obstruction. With the single port lance, replacement would be necessary which would interrupt the treatment process. Whereas, if one of the dual ports became unrepairably clogged in the present invention the treatment process of the metals need not be interrupted because the other of the exit ports will still be operable to complete the treatment process.
Because there are two exit ports in the present invention dual port lance versus the single exit port in the conventional single port lance, and each exit port of the present invention has increased flow in comparison with the conventional lances, less time is necessary for every heat. The fact that less time per heat is necessary allows for more heats to be completed during the life of the dual port lance. Therefore, less dual port lances are necessary for the same desulfurization process done by a conventional single port lance.